When you use the BE module to send an email message, there is a link to the "Other Tokens" in the Messaging area of a new campaign.
Expand this and you will see:

Name

Description

Sample

unsubscribe

Insert an unsubscribe link into the message

[unsubscribe- here]

unsubscribe_img

Insert an unsubscribe image link into the message

[unsubscribe_img-/Portals/0/unsubscribe.png]

viewonline

Insert an unsubscribe image link into the message

[unsubscribe- here]

You have use the unsubscribe token, not the unsubscribe_img token. This is why it is attempting to display everything after the word unsubscribe as text - like in the manual where we have the example [unsubscribe-click here].